Providing certificate matching in a system and method for searching and  retrieving certificates

ABSTRACT

A system and method for searching and retrieving certificates, which may be used in the processing of encoded messages. In one broad aspect, certificate identification data that uniquely identifies a certificate associated with a message is generated. The certificate identification data can then be used to determine whether the certificate is stored on a computing device. Only the certificate identification data is needed to facilitate the determination alleviating the need for a user to download the entire message to the computing device in order to make the determination.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/405,551, filed on Mar. 17, 2009, which is a divisional of U.S. patentapplication Ser. No. 10/931,109, filed on Sep. 1, 2004, which issued topatent as U.S. Pat. No. 7,549,043. The entire contents of U.S.application Ser. No. 10/931,109 and U.S. patent application Ser. No.12/405,551 are hereby incorporated by reference.

FIELD OF THE INVENTION

The invention relates generally to the processing of messages, such ase-mail messages, and more specifically to a system and method forsearching and retrieving certificates used in the processing of encodedmessages.

BACKGROUND OF THE INVENTION

Electronic mail (“e-mail”) messages may be encoded using one of a numberof known protocols. Some of these protocols, such as Secure MultipleInternet Mail Extensions (“S/MIME”) for example, rely on public andprivate encryption keys to provide confidentiality and integrity, and ona Public Key Infrastructure (PKI) to communicate information thatprovides authentication and authorization. Data encrypted using aprivate key of a private key/public key pair can only be decrypted usingthe corresponding public key of the pair, and vice-versa. Theauthenticity of public keys used in the encoding of messages isvalidated using certificates. In particular, if a user of a computingdevice wishes to encrypt a message before the message is sent to aparticular individual, the user will require a certificate for thatindividual. That certificate will typically comprise the public key ofthe individual, as well as other identification-related information.Similarly, if a user of a computing device wishes to authenticate thesender of a signed message, the user will require a certificate for thatsender.

If the requisite certificate is not already stored on the user'scomputing device, the certificate must first be retrieved. Searching forand retrieving a specific certificate is a process that generallyinvolves querying a certificate server by having the user manually enterthe name and/or e-mail address of the individual for which a certificateis requested in a search form displayed on the computing device.Generally, certificates located in the search are then temporarilydownloaded to the computing device for consideration, and a list oflocated certificates may then be displayed to the user. Selectedcertificates in the list may then be manually identified by a user forstorage in a non-volatile store of the computing device, for potentialfuture use.

Consider an implementation where the user's computing device is a mobiledevice. When a message is received at a message server and is madeavailable for downloading to the mobile device, the message is typicallyonly transmitted to the mobile device in successive data blocks of apre-defined size, in order to conserve bandwidth. More specifically, afirst block of the message (e.g. 2 KB of data) is downloaded to themobile device, and if the user wishes to receive more of the message,the user can request that further blocks be downloaded to the mobiledevice, until the entire message has been downloaded to the mobiledevice or until some pre-defined limit on the message download isreached.

If the received message is a signed S/MIME message, for example, inorder to verify the integrity of the message and authenticate theidentity of the sender, the certificate of the sender is required. Insome cases, the requisite certificate may accompany the message, withthe certificate typically being attached to the end of the message.Alternatively, the requisite certificate may not accompany the message,but one or more certificate identifiers that identify the certificateused in the signing is provided, also typically at the end of themessage. The identified certificate can then be retrieved from either acertificate store on the mobile device if the certificate is alreadystored therein, or a certificate server from which the certificate canbe downloaded as noted above.

In order to obtain the certificate or the certificate identifiers for amessage, the entire message must typically be downloaded to the mobiledevice. Unfortunately, downloading entire messages simply to retrievethe certificate information can be a time-consuming and expensive task(e.g. with respect to bandwidth). On the other hand, if only a smallpart of the message has been downloaded to the mobile device, or if themessage is too long and cannot be downloaded to the mobile device due toan imposed limit, it may not be possible to identify the certificatethat is required to verify the integrity of the received message and toauthenticate the identity of the sender with any certainty.

SUMMARY OF THE INVENTION

Embodiments of the invention are generally directed to a system andmethod for more efficiently searching and retrieving certificates, inwhich the requisite certificate can be identified without requiring thesender's message to be downloaded in its entirety to the user'scomputing device (e.g. a mobile device). In particular, the system andmethod facilitates a determination of the requisite certificate fromcertificates located in a search of one or more certificate servers.

In one broad aspect of the invention, there is provided a method ofsearching and retrieving certificates relating to a message received bya user from a sender, the message comprising data identifying a sendercertificate associated therewith, wherein certificate identificationdata that uniquely identifies the sender certificate can be generatedfrom the message, and wherein the method comprises the steps of:receiving at least a part of the message and certificate identificationdata at a computing device; providing a certificate search request forcertificates associated with the sender; performing a search on one ormore certificate servers, wherein at least one query is submitted to theone or more certificate servers to request retrieval of locatedcertificates satisfying the certificate search request; retrieving atleast one located certificate from the one or more certificate servers;processing each located certificate retrieved, using the certificateidentification data, to determine if the respective located certificateis the sender certificate associated with the message; and storing alocated certificate on the computing device, if the located certificateis the sender certificate associated with the message as determined atthe determining step.

In another broad aspect, the generated certificate identification dataincludes a serial number and issuer data for the sender certificate; andthe processing step comprises parsing each located certificate retrievedto obtain the respective serial number and issuer data, and comparingthe respective serial number and issuer data to the certificateidentification data.

In another broad aspect, the generated certificate identification dataincludes a hash of at least a part of the sender certificate; and theprocessing step comprises applying a hash algorithm to each locatedcertificate retrieved to obtain the respective hash, and comparing therespective hash to the certificate identification data.

In another broad aspect of the invention, there is provided a system forsearching and retrieving certificates relating to a message received bya user from a sender, the message comprising data identifying a sendercertificate associated therewith, the system comprising: a messagemanagement server adapted to generate certificate identification datafrom the message, wherein the certificate identification data uniquelyidentifies the sender certificate; a mobile device adapted to receive atleast a part of the message, and the certificate identification data,from the message management server; and a mobile data server adapted toreceive a search request for certificates associated with the senderfrom the mobile device, perform a search on one or more certificateservers by querying the one or more certificate servers for locatedcertificates satisfying the search request, and retrieve locatedcertificates from the one or more certificate servers; wherein at leastone of the mobile device and the mobile data server is further adaptedto process each located certificate retrieved at the mobile data serverto determine, using the certification identification data, if therespective located certificate is the sender certificate associated withthe message; and wherein the mobile device provides one or morecertificate stores to store a located certificate determined to be thesender certificate associated with the message.

In another broad aspect, there is provided a method of searching andretrieving certificates relating to a message received by a user from asender, the message comprising data identifying a sender certificateassociated therewith, wherein the method comprises the steps of:generating certificate identification data for the sender certificatefrom the data in the received message identifying the sendercertificate, wherein the certificate identification data uniquelyidentifies the sender certificate; receiving certificate identificationdata at a computing device; and determining whether the sendercertificate is stored on the computing device, by generating certificateidentification data associated with each of a plurality of certificatesstored on the computing device, and comparing generated certificateidentification data for each of the plurality of stored certificates tothe certificate identification data generated for the sender certificateto identify a stored certificate matching the sender certificate.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of embodiments of the invention, and to showmore clearly how it may be carried into effect, reference will now bemade, by way of example, to the accompanying drawings in which:

FIG. 1 is a block diagram of a mobile device in one exampleimplementation;

FIG. 2 is a block diagram of a communication subsystem component of themobile device of FIG. 1;

FIG. 3 is a block diagram of a node of a wireless network;

FIG. 4 is a block diagram illustrating components of a host system inone example configuration;

FIG. 5 is a block diagram showing an example of a certificate chain;

FIG. 6 is a block diagram illustrating components of an example of anencoded message;

FIG. 7A is a flowchart illustrating steps in a method of searching andretrieving certificates in an embodiment of the invention; and

FIG. 7B is a flowchart illustrating steps in a method of searching andretrieving certificates in another embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Some embodiments of the invention make use of a mobile station. A mobilestation is a two-way communication device with advanced datacommunication capabilities having the capability to communicate withother computer systems, and is also referred to herein generally as amobile device. A mobile device may also include the capability for voicecommunications. Depending on the functionality provided by a mobiledevice, it may be referred to as a data messaging device, a two-waypager, a cellular telephone with data messaging capabilities, a wirelessInternet appliance, or a data communication device (with or withouttelephony capabilities). A mobile device communicates with other devicesthrough a network of transceiver stations.

To aid the reader in understanding the structure of a mobile device andhow it communicates with other devices, reference is made to FIGS. 1through 3.

Referring first to FIG. 1, a block diagram of a mobile device in oneexample implementation is shown generally as 100. Mobile device 100comprises a number of components, the controlling component beingmicroprocessor 102. Microprocessor 102 controls the overall operation ofmobile device 100. Communication functions, including data and voicecommunications, are performed through communication subsystem 104.Communication subsystem 104 receives messages from and sends messages toa wireless network 200. In this example implementation of mobile device100, communication subsystem 104 is configured in accordance with theGlobal System for Mobile Communication (GSM) and General Packet RadioServices (GPRS) standards. The GSM/GPRS wireless network is usedworldwide and it is expected that these standards will be supersededeventually by Enhanced Data GSM Environment (EDGE) and Universal MobileTelecommunications Service (UMTS). New standards are still beingdefined, but it is believed that they will have similarities to thenetwork behaviour described herein, and it will also be understood bypersons skilled in the art that the invention is intended to use anyother suitable standards that are developed in the future. The wirelesslink connecting communication subsystem 104 with network 200 representsone or more different Radio Frequency (RF) channels, operating accordingto defined protocols specified for GSM/GPRS communications. With newernetwork protocols, these channels are capable of supporting both circuitswitched voice communications and packet switched data communications.

Although the wireless network associated with mobile device 100 is aGSM/GPRS wireless network in one example implementation of mobile device100, other wireless networks may also be associated with mobile device100 in variant implementations. Different types of wireless networksthat may be employed include, for example, data-centric wirelessnetworks, voice-centric wireless networks, and dual-mode networks thatcan support both voice and data communications over the same physicalbase stations. Combined dual-mode networks include, but are not limitedto, Code Division Multiple Access (CDMA) or CDMA2000 networks, GSM/GPRSnetworks (as mentioned above), and future third-generation (3G) networkslike EDGE and UMTS. Some older examples of data-centric networks includethe Mobitex™ Radio Network and the DataTAC™ Radio Network. Examples ofolder voice-centric data networks include Personal Communication Systems(PCS) networks like GSM and Time Division Multiple Access (TDMA)systems.

Microprocessor 102 also interacts with additional subsystems such as aRandom Access Memory (RAM) 106, flash memory 108, display 110, auxiliaryinput/output (I/O) subsystem 112, serial port 114, keyboard 116, speaker118, microphone 120, short-range communications 122 and other devices124.

Some of the subsystems of mobile device 100 performcommunication-related functions, whereas other subsystems may provide“resident” or on-device functions. By way of example, display 110 andkeyboard 116 may be used for both communication-related functions, suchas entering a text message for transmission over network 200, anddevice-resident functions such as a calculator or task list. Operatingsystem software used by microprocessor 102 is typically stored in apersistent store such as flash memory 108, which may alternatively be aread-only memory (ROM) or similar storage element (not shown). Thoseskilled in the art will appreciate that the operating system, specificdevice applications, or parts thereof, may be temporarily loaded into avolatile store such as RAM 106.

Mobile device 100 may send and receive communication signals overnetwork 200 after required network registration or activation procedureshave been completed. Network access is associated with a subscriber oruser of a mobile device 100. To identify a subscriber, mobile device 100requires a Subscriber Identity Module or “SIM” card 126 to be insertedin a SIM interface 128 in order to communicate with a network. SIM 126is one type of a conventional “smart card” used to identify a subscriberof mobile device 100 and to personalize the mobile device 100, amongother things. Without SIM 126, mobile device 100 is not fullyoperational for communication with network 200. By inserting SIM 126into SIM interface 128, a subscriber can access all subscribed services.Services could include: web browsing and messaging such as e-mail, voicemail, Short Message Service (SMS), and Multimedia Messaging Services(MMS). More advanced services may include: point of sale, field serviceand sales force automation. SIM 126 includes a processor and memory forstoring information. Once SIM 126 is inserted in SIM interface 128, itis coupled to microprocessor 102. In order to identify the subscriber,SIM 126 contains some user parameters such as an International MobileSubscriber Identity (IMSI). An advantage of using SIM 126 is that asubscriber is not necessarily bound by any single physical mobiledevice. SIM 126 may store additional subscriber information for a mobiledevice as well, including datebook (or calendar) information and recentcall information.

Mobile device 100 is a battery-powered device and includes a batteryinterface 132 for receiving one or more rechargeable batteries 130.Battery interface 132 is coupled to a regulator (not shown), whichassists battery 130 in providing power V+ to mobile device 100. Althoughcurrent technology makes use of a battery, future technologies such asmicro fuel cells may provide the power to mobile device 100.

Microprocessor 102, in addition to its operating system functions,enables execution of software applications on mobile device 100. A setof applications that control basic device operations, including data andvoice communication applications, will normally be installed on mobiledevice 100 during its manufacture. Another application that may beloaded onto mobile device 100 would be a personal information manager(PIM). A PIM has functionality to organize and manage data items ofinterest to a subscriber, such as, but not limited to, e-mail, calendarevents, voice mails, appointments, and task items. A PIM application hasthe ability to send and receive data items via wireless network 200. PIMdata items may be seamlessly integrated, synchronized, and updated viawireless network 200 with the mobile device subscriber's correspondingdata items stored and/or associated with a host computer system. Thisfunctionality creates a mirrored host computer on mobile device 100 withrespect to such items. This can be particularly advantageous where thehost computer system is the mobile device subscriber's office computersystem.

Additional applications may also be loaded onto mobile device 100through network 200, auxiliary I/O subsystem 112, serial port 114,short-range communications subsystem 122, or any other suitablesubsystem 124. This flexibility in application installation increasesthe functionality of mobile device 100 and may provide enhancedon-device functions, communication-related functions, or both. Forexample, secure communication applications may enable electroniccommerce functions and other such financial transactions to be performedusing mobile device 100.

Serial port 114 enables a subscriber to set preferences through anexternal device or software application and extends the capabilities ofmobile device 100 by providing for information or software downloads tomobile device 100 other than through a wireless communication network.The alternate download path may, for example, be used to load anencryption key onto mobile device 100 through a direct and thus reliableand trusted connection to provide secure device communication.

Short-range communications subsystem 122 provides for communicationbetween mobile device 100 and different systems or devices, without theuse of network 200. For example, subsystem 122 may include an infrareddevice and associated circuits and components for short-rangecommunication. Examples of short range communication would includestandards developed by the Infrared Data Association (IrDA), Bluetooth,and the 802.11 family of standards developed by IEEE.

In use, a received signal such as a text message, an e-mail message, orweb page download will be processed by communication subsystem 104 andinput to microprocessor 102. Microprocessor 102 will then process thereceived signal for output to display 110 or alternatively to auxiliaryI/O subsystem 112. A subscriber may also compose data items, such ase-mail messages, for example, using keyboard 116 in conjunction withdisplay 110 and possibly auxiliary I/O subsystem 112. Auxiliarysubsystem 112 may include devices such as: a touch screen, mouse, trackball, infrared fingerprint detector, or a roller wheel with dynamicbutton pressing capability. Keyboard 116 is an alphanumeric keyboardand/or telephone-type keypad. A composed item may be transmitted overnetwork 200 through communication subsystem 104.

For voice communications, the overall operation of mobile device 100 issubstantially similar, except that the received signals would be outputto speaker 118, and signals for transmission would be generated bymicrophone 120. Alternative voice or audio I/O subsystems, such as avoice message recording subsystem, may also be implemented on mobiledevice 100. Although voice or audio signal output is accomplishedprimarily through speaker 118, display 110 may also be used to provideadditional information such as the identity of a calling party, durationof a voice call, or other voice call related information.

Referring now to FIG. 2, a block diagram of the communication subsystemcomponent 104 of FIG. 1 is shown. Communication subsystem 104 comprisesa receiver 150, a transmitter 152, one or more embedded or internalantenna elements 154, 156, Local Oscillators (LOs) 158, and a processingmodule such as a Digital Signal Processor (DSP) 160.

The particular design of communication subsystem 104 is dependent uponthe network 200 in which mobile device 100 is intended to operate, thusit should be understood that the design illustrated in FIG. 2 servesonly as one example. Signals received by antenna 154 through network 200are input to receiver 150, which may perform such common receiverfunctions as signal amplification, frequency down conversion, filtering,channel selection, and analog-to-digital (A/D) conversion. A/Dconversion of a received signal allows more complex communicationfunctions such as demodulation and decoding to be performed in DSP 160.In a similar manner, signals to be transmitted are processed, includingmodulation and encoding, by DSP 160. These DSP-processed signals areinput to transmitter 152 for digital-to-analog (D/A) conversion,frequency up conversion, filtering, amplification and transmission overnetwork 200 via antenna 156. DSP 160 not only processes communicationsignals, but also provides for receiver and transmitter control. Forexample, the gains applied to communication signals in receiver 150 andtransmitter 152 may be adaptively controlled through automatic gaincontrol algorithms implemented in DSP 160.

The wireless link between mobile device 100 and a network 200 maycontain one or more different channels, typically different RF channels,and associated protocols used between mobile device 100 and network 200.A RF channel is a limited resource that must be conserved, typically dueto limits in overall bandwidth and limited battery power of mobiledevice 100.

When mobile device 100 is fully operational, transmitter 152 istypically keyed or turned on only when it is sending to network 200 andis otherwise turned off to conserve resources. Similarly, receiver 150is periodically turned off to conserve power until it is needed toreceive signals or information (if at all) during designated timeperiods.

Referring now to FIG. 3, a block diagram of a node of a wireless networkis shown as 202. In practice, network 200 comprises one or more nodes202. Mobile device 100 communicates with a node 202 within wirelessnetwork 200. In the example implementation of FIG. 3, node 202 isconfigured in accordance with General Packet Radio Service (GPRS) andGlobal Systems for Mobile (GSM) technologies. Node 202 includes a basestation controller (BSC) 204 with an associated tower station 206, aPacket Control Unit (PCU) 208 added for GPRS support in GSM, a MobileSwitching Center (MSC) 210, a Home Location Register (HLR) 212, aVisitor Location Registry (VLR) 214, a Serving GPRS Support Node (SGSN)216, a Gateway GPRS Support Node (GGSN) 218, and a Dynamic HostConfiguration Protocol (DHCP) 220. This list of components is not meantto be an exhaustive list of the components of every node 202 within aGSM/GPRS network, but rather a list of components that are commonly usedin communications through network 200.

In a GSM network, MSC 210 is coupled to BSC 204 and to a landlinenetwork, such as a Public Switched Telephone Network (PSTN) 222 tosatisfy circuit switched requirements. The connection through PCU 208,SGSN 216 and GGSN 218 to the public or private network (Internet) 224(also referred to herein generally as a shared network infrastructure)represents the data path for GPRS capable mobile devices. In a GSMnetwork extended with GPRS capabilities, BSC 204 also contains a PacketControl Unit (PCU) 208 that connects to SGSN 216 to controlsegmentation, radio channel allocation and to satisfy packet switchedrequirements. To track mobile device location and availability for bothcircuit switched and packet switched management, HLR 212 is sharedbetween MSC 210 and SGSN 216. Access to VLR 214 is controlled by MSC210.

Station 206 is a fixed transceiver station. Station 206 and BSC 204together form the fixed transceiver equipment. The fixed transceiverequipment provides wireless network coverage for a particular coveragearea commonly referred to as a “cell”. The fixed transceiver equipmenttransmits communication signals to and receives communication signalsfrom mobile devices within its cell via station 206. The fixedtransceiver equipment normally performs such functions as modulation andpossibly encoding and/or encryption of signals to be transmitted to themobile device in accordance with particular, usually predetermined,communication protocols and parameters, under control of its controller.The fixed transceiver equipment similarly demodulates and possiblydecodes and decrypts, if necessary, any communication signals receivedfrom mobile device 100 within its cell. Communication protocols andparameters may vary between different nodes. For example, one node mayemploy a different modulation scheme and operate at differentfrequencies than other nodes.

For all mobile devices 100 registered with a specific network, permanentconfiguration data such as a user profile is stored in HLR 212. HLR 212also contains location information for each registered mobile device andcan be queried to determine the current location of a mobile device. MSC210 is responsible for a group of location areas and stores the data ofthe mobile devices currently in its area of responsibility in VLR 214.Further VLR 214 also contains information on mobile devices that arevisiting other networks. The information in VLR 214 includes part of thepermanent mobile device data transmitted from HLR 212 to VLR 214 forfaster access. By moving additional information from a remote HLR 212node to VLR 214, the amount of traffic between these nodes can bereduced so that voice and data services can be provided with fasterresponse times and at the same time requiring less use of computingresources.

SGSN 216 and GGSN 218 are elements added for GPRS support; namely packetswitched data support, within GSM. SGSN 216 and MSC 210 have similarresponsibilities within wireless network 200 by keeping track of thelocation of each mobile device 100. SGSN 216 also performs securityfunctions and access control for data traffic on network 200. GGSN 218provides internetworking connections with external packet switchednetworks and connects to one or more SGSN's 216 via an Internet Protocol(IP) backbone network operated within the network 200. During normaloperations, a given mobile device 100 must perform a “GPRS Attach” toacquire an IP address and to access data services. This requirement isnot present in circuit switched voice channels as Integrated ServicesDigital Network (ISDN) addresses are used for routing incoming andoutgoing calls. Currently, all GPRS capable networks use private,dynamically assigned IP addresses, thus requiring a DHCP server 220connected to the GGSN 218. There are many mechanisms for dynamic IPassignment, including using a combination of a Remote AuthenticationDial-In User Service (RADIUS) server and DHCP server. Once the GPRSAttach is complete, a logical connection is established from a mobiledevice 100, through PCU 208, and SGSN 216 to an Access Point Node (APN)within GGSN 218. The APN represents a logical end of an IP tunnel thatcan either access direct Internet compatible services or private networkconnections. The APN also represents a security mechanism for network200, insofar as each mobile device 100 must be assigned to one or moreAPNs and mobile devices 100 cannot exchange data without firstperforming a GPRS Attach to an APN that it has been authorized to use.The APN may be considered to be similar to an Internet domain name suchas “myconnection.wireless.com”.

Once the GPRS Attach is complete, a tunnel is created and all traffic isexchanged within standard IP packets using any protocol that can besupported in IP packets. This includes tunneling methods such as IP overIP as in the case with some IPSecurity (IPsec) connections used withVirtual Private Networks (VPN). These tunnels are also referred to asPacket Data Protocol (PDP) Contexts and there are a limited number ofthese available in the network 200. To maximize use of the PDP Contexts,network 200 will run an idle timer for each PDP Context to determine ifthere is a lack of activity. When a mobile device 100 is not using itsPDP Context, the PDP Context can be deallocated and the IP addressreturned to the IP address pool managed by DHCP server 220.

Referring now to FIG. 4, a block diagram illustrating components of ahost system in one example configuration is shown. Host system 250 willtypically be a corporate office or other local area network (LAN), butmay instead be a home office computer or some other private system, forexample, in variant implementations. In this example shown in FIG. 4,host system 250 is depicted as a LAN of an organization to which a userof mobile device 100 belongs.

LAN 250 comprises a number of network components connected to each otherby LAN connections 260. For instance, a user's desktop computer 262 awith an accompanying cradle 264 for the user's mobile device 100 issituated on LAN 250. Cradle 264 for mobile device 100 may be coupled tocomputer 262 a by a serial or a Universal Serial Bus (USB) connection,for example. Other user computers 262 b are also situated on LAN 250,and each may or may not be equipped with an accompanying cradle 264 fora mobile device. Cradle 264 facilitates the loading of information (e.g.PIM data, private symmetric encryption keys to facilitate securecommunications between mobile device 100 and LAN 250) from user computer262 a to mobile device 100, and may be particularly useful for bulkinformation updates often performed in initializing mobile device 100for use. The information downloaded to mobile device 100 may includecertificates used in the exchange of messages. It will be understood bypersons skilled in the art that user computers 262 a, 262 b willtypically be also connected to other peripheral devices not explicitlyshown in FIG. 4.

Embodiments of the invention relate generally to the processing ofmessages, such as e-mail messages, and some embodiments relate generallyto the communication of such messages to and from mobile device 100.Accordingly, only a subset of network components of LAN 250 are shown inFIG. 4 for ease of exposition, and it will be understood by personsskilled in the art that LAN 250 will comprise additional components notexplicitly shown in FIG. 4, for this example configuration. Moregenerally, LAN 250 may represent a smaller part of a larger network [notshown] of the organization, and may comprise different components and/orbe arranged in different topologies than that shown in the example ofFIG. 4.

In this example, mobile device 100 communicates with LAN 250 through anode 202 of wireless network 200 and a shared network infrastructure 224such as a service provider network or the public Internet. Access to LAN250 may be provided through one or more routers [not shown], andcomputing devices of LAN 250 may operate from behind a firewall or proxyserver 266.

In a variant implementation, LAN 250 comprises a wireless VPN router[not shown] to facilitate data exchange between the LAN 250 and mobiledevice 100. The concept of a wireless VPN router is new in the wirelessindustry and implies that a VPN connection can be established directlythrough a specific wireless network to mobile device 100. Thepossibility of using a wireless VPN router has only recently beenavailable and could be used when the new Internet Protocol (IP) Version6 (IPV6) arrives into IP-based wireless networks. This new protocol willprovide enough IP addresses to dedicate an IP address to every mobiledevice, making it possible to push information to a mobile device at anytime. An advantage of using a wireless VPN router is that it could be anoff-the-shelf VPN component, not requiring a separate wireless gatewayand separate wireless infrastructure to be used. A VPN connection wouldpreferably be a Transmission Control Protocol (TCP)/IP or User DatagramProtocol (UDP)/IP connection to deliver the messages directly to mobiledevice 100 in this variant implementation.

Messages intended for a user of mobile device 100 are initially receivedby a message server 268 of LAN 250. Such messages may originate from anyof a number of sources. For instance, a message may have been sent by asender from a computer 262 b within LAN 250, from a different mobiledevice [not shown] connected to wireless network 200 or to a differentwireless network, or from a different computing device or other devicecapable of sending messages, via the shared network infrastructure 224,and possibly through an application service provider (ASP) or Internetservice provider (ISP), for example.

Message server 268 typically acts as the primary interface for theexchange of messages, particularly e-mail messages, within theorganization and over the shared network infrastructure 224. Each userin the organization that has been set up to send and receive messages istypically associated with a user account managed by message server 268.One example of a message server 268 is a Microsoft Exchange™ Server. Insome implementations, LAN 250 may comprise multiple message servers 268.Message server 268 may also be adapted to provide additional functionsbeyond message management, including the management of data associatedwith calendars and task lists, for example.

When messages are received by message server 268, they are typicallystored in a message store [not explicitly shown], from which messagescan be subsequently retrieved and delivered to users. For instance, ane-mail client application operating on a user's computer 262 a mayrequest the e-mail messages associated with that user's account storedon message server 268. These messages would then typically be retrievedfrom message server 268 and stored locally on computer 262 a.

When operating mobile device 100, the user may wish to have e-mailmessages retrieved for delivery to the handheld. An e-mail clientapplication operating on mobile device 100 may also request messagesassociated with the user's account from message server 268. The e-mailclient may be configured (either by the user or by an administrator,possibly in accordance with an organization's information technology(IT) policy) to make this request at the direction of the user, at somepre-defined time interval, or upon the occurrence of some pre-definedevent. In some implementations, mobile device 100 is assigned its owne-mail address, and messages addressed specifically to mobile device 100are automatically redirected to mobile device 100 as they are receivedby message server 268.

To facilitate the wireless communication of messages and message-relateddata between mobile device 100 and components of LAN 250, a number ofwireless communications support components 270 may be provided. In thisexample implementation, wireless communications support components 270comprise a message management server 272, for example. Messagemanagement server 272 is used to specifically provide support for themanagement of messages, such as e-mail messages, that are to be handledby mobile devices. Generally, while messages are still stored on messageserver 268, message management server 272 can be used to control when,if, and how messages should be sent to mobile device 100. Messagemanagement server 272 also facilitates the handling of messages composedon mobile device 100, which are sent to message server 268 forsubsequent delivery.

For example, message management server 272 may: monitor the user's“mailbox” (e.g. the message store associated with the user's account onmessage server 268) for new e-mail messages; apply user-definablefilters to new messages to determine if and how the messages will berelayed to the user's mobile device 100; compress and encrypt newmessages (e.g. using an encryption technique such as Data EncryptionStandard (DES) or Triple DES) and push them to mobile device 100 via theshared network infrastructure 224 and wireless network 200; and receivemessages composed on mobile device 100 (e.g. encrypted using TripleDES), decrypt and decompress the composed messages, re-format thecomposed messages if desired so that they will appear to have originatedfrom the user's computer 262 a, and re-route the composed messages tomessage server 268 for delivery.

Certain properties or restrictions associated with messages that are tobe sent from and/or received by mobile device 100 can be defined (e.g.by an administrator in accordance with IT policy) and enforced bymessage management server 272. These may include whether mobile device100 may receive encrypted and/or signed messages, minimum encryption keysizes, whether outgoing messages must be encrypted and/or signed, andwhether copies of all secure messages sent from mobile device 100 are tobe sent to a pre-defined copy address, for example.

Message management server 272 may also be adapted to provide othercontrol functions, such as only pushing certain message information orpre-defined portions (e.g. “blocks”) of a message stored on messageserver 268 to mobile device 100. For example, when a message isinitially retrieved by mobile device 100 from message server 268,message management server 272 is adapted to push only the first part ofa message to mobile device 100, with the part being of a pre-definedsize (e.g. 2 KB). The user can then request more of the message, to bedelivered in similar-sized blocks by message management server 272 tomobile device 100, possibly up to a maximum pre-defined message size.

Accordingly, message management server 272 facilitates better controlover the type of data and the amount of data that is communicated tomobile device 100, and can help to minimize potential waste of bandwidthor other resources.

It will be understood by persons skilled in the art that messagemanagement server 272 need not be implemented on a separate physicalserver in LAN 250 or other network. For example, some or all of thefunctions associated with message management server 272 may beintegrated with message server 268, or some other server in LAN 250.Furthermore, LAN 250 may comprise multiple message management servers272, particularly in variant implementations where a large number ofmobile devices need to be supported.

Embodiments of the invention relate generally to the processing ofencoded messages, such as e-mail messages that are encrypted and/orsigned. While Simple Mail Transfer Protocol (SMTP), RFC822 headers, andMultipurpose Internet Mail Extensions (MIME) body parts may be used todefine the format of a typical e-mail message not requiring encoding,Secure/MIME (S/MIME), a version of the MIME protocol, may be used in thecommunication of encoded messages (i.e. in secure messagingapplications). S/MIME enables end-to-end authentication andconfidentiality, and protects data integrity and privacy from the timean originator of a message sends a message until it is decoded and readby the message recipient. Other known standards and protocols may beemployed to facilitate secure message communication, such as Pretty GoodPrivacy™ (PGP), OpenPGP, and others known in the art.

Secure messaging protocols such as S/MIME rely on public and privateencryption keys to provide confidentiality and integrity, and on aPublic Key Infrastructure (PKI) to communicate information that providesauthentication and authorization. Data encrypted using a private key ofa private key/public key pair can only be decrypted using thecorresponding public key of the pair, and vice-versa. Private keyinformation is never made public, whereas public key information isshared.

For example, if a sender wishes to send a message to a recipient inencrypted form, the recipient's public key is used to encrypt a message,which can then be decrypted only using the recipient's private key.Alternatively, in some encoding techniques, a one-time session key isgenerated and used to encrypt the body of a message, typically with asymmetric encryption technique (e.g. Triple DES). The session key isthen encrypted using the recipient's public key (e.g. with a public keyencryption algorithm such as RSA), which can then be decrypted onlyusing the recipient's private key. The decrypted session key can then beused to decrypt the message body. The message header may be used tospecify the particular encryption scheme that must be used to decryptthe message. Other encryption techniques based on public keycryptography may be used in variant implementations. However, in each ofthese cases, only the recipient's private key may be used to facilitatedecryption of the message, and in this way, the confidentiality ofmessages can be maintained.

As a further example, a sender may sign a message using a digitalsignature. A digital signature is a digest of the message (e.g. a hashof the message) encrypted using the sender's private key, which can thenbe appended to the outgoing message. To verify the signature of themessage when received, the recipient uses the same technique as thesender (e.g. using the same standard hash algorithm) to obtain a digestof the received message. The recipient also uses the sender's public keyto decrypt the digital signature, in order to obtain what should be amatching digest for the received message. If the digests of the receivedmessage do not match, this suggests that either the message content waschanged during transport and/or the message did not originate from thesender whose public key was used for verification. By verifying adigital signature in this way, authentication of the sender and messageintegrity can be maintained.

An encoded message may be encrypted, signed, or both encrypted andsigned. The authenticity of public keys used in these operations isvalidated using certificates. A certificate is a digital document issuedby a certificate authority (CA). Certificates are used to authenticatethe association between users and their public keys, and essentially,provides a level of trust in the authenticity of the users' public keys.Certificates contain information about the certificate holder, withcertificate contents typically formatted in accordance with an acceptedstandard (e.g. X.509).

Consider FIG. 5, in which an example certificate chain 300 is shown.Certificate 310 issued to “John Smith” is an example of a certificateissued to an individual, which may be referred to as an end entitycertificate. End entity certificate 310 typically identifies thecertificate holder 312 (i.e. John Smith in this example) and the issuerof the certificate 314, and includes a digital signature of the issuer316 and the certificate holder's public key 318. Certificate 310 willalso typically include other information and attributes that identifythe certificate holder (e.g. e-mail address, organization name,organizational unit name, location, etc.). When the individual composesa message to be sent to a recipient, it is customary to include thatindividual's certificate 300 with the message.

For a public key to be trusted, its issuing organization must betrusted. The relationship between a trusted CA and a user's public keycan be represented by a series of related certificates, also referred toas a certificate chain. The certificate chain can be followed todetermine the validity of a certificate.

For instance, in the example certificate chain 300 shown in FIG. 5, therecipient of a message purported to be sent by John Smith may wish toverify the trust status of certificate 310 attached to the receivedmessage. To verify the trust status of certificate 310 on a recipient'scomputing device (e.g. computer 262 a of FIG. 4) for example, thecertificate 320 of issuer ABC is obtained, and used to verify thatcertificate 310 was indeed signed by issuer ABC. Certificate 320 mayalready be stored in a certificate store on the computing device, or itmay need to be retrieved from a certificate source (e.g. LDAP server 284of FIG. 4 or some other public or private LDAP server). If certificate320 is already stored in the recipient's computing device and thecertificate has been designated as trusted by the recipient, thencertificate 310 is considered to be trusted since it chains to a stored,trusted certificate.

However, in the example shown in FIG. 5, certificate 330 is alsorequired to verify the trust of certificate 310. Certificate 330 isself-signed, and is referred to as a “root certificate”. Accordingly,certificate 320 may be referred to as an “intermediate certificate” incertificate chain 300; any given certificate chain to a rootcertificate, assuming a chain to the root certificate can be determinedfor a particular end entity certificate, may contain zero, one, ormultiple intermediate certificates. If certificate 330 is a rootcertificate issued by a trusted source (from a large certificateauthority such as Verisign or Entrust, for example), then certificate310 may be considered to be trusted since it chains to a trustedcertificate. The implication is that both the sender and the recipientof the message trust the source of the root certificate 330. If acertificate cannot be chained to a trusted certificate, the certificatemay be considered to be “not trusted”.

Certificate servers store information about certificates and listsidentifying certificates that have been revoked. These certificateservers can be accessed to obtain certificates and to verify certificateauthenticity and revocation status. For example, a Lightweight DirectoryAccess Protocol (LDAP) server may be used to obtain certificates, and anOnline Certificate Status Protocol (OCSP) server may be used to verifycertificate revocation status.

Standard e-mail security protocols typically facilitate secure messagetransmission between non-mobile computing devices (e.g. computers 262 a,262 b of FIG. 4; remote desktop devices). Referring again to FIG. 4, inorder that signed messages received from senders may be read from mobiledevice 100 and encrypted messages be sent to those senders, mobiledevice 100 is adapted to store certificates and associated public keysof other individuals. Certificates stored on a user's computer 262 awill typically be downloaded from computer 262 a to mobile device 100through cradle 264, for example.

Certificates stored on computer 262 a and downloaded to mobile device100 are not limited to certificates associated with individuals but mayalso include certificates issued to CAs, for example. Certaincertificates stored in computer 262 a and/or mobile device 100 can alsobe explicitly designated as “trusted” by the user. Accordingly, when acertificate is received by a user on mobile device 100, it can beverified on mobile device 100 by matching the certificate with onestored on mobile device 100 and designated as trusted, or otherwisedetermined to be chained to a trusted certificate.

Mobile device 100 may also be adapted to store the private key of thepublic key/private key pair associated with the user, so that the userof mobile device 100 can sign outgoing messages composed on mobiledevice 100, and decrypt messages sent to the user encrypted with theuser's public key. The private key may be downloaded to mobile device100 from the user's computer 262 a through cradle 264, for example. Theprivate key is preferably exchanged between the computer 262 a andmobile device 100 so that the user may share one identity and one methodfor accessing messages.

User computers 262 a, 262 b can obtain certificates from a number ofsources, for storage on computers 262 a, 262 b and/or mobile devices(e.g. mobile device 100). These certificate sources may be private (e.g.dedicated for use within an organization) or public, may reside locallyor remotely, and may be accessible from within an organization's privatenetwork or through the Internet, for example. In the example shown inFIG. 4, multiple PKI servers 280 associated with the organization resideon LAN 250. PKI servers 280 include a CA server 282 for issuingcertificates, an LDAP server 284 used to search for and downloadcertificates (e.g. for individuals within the organization), and an OCSPserver 286 used to verify the revocation status of certificates.

Certificates may be retrieved from LDAP server 284 by a user computer262 a, for example, to be downloaded to mobile device 100 via cradle264. However, in a variant implementation, LDAP server 284 may beaccessed directly (i.e. “over the air” in this context) by mobile device100, and mobile device 100 may search for and retrieve individualcertificates through a mobile data server 288. Similarly, mobile dataserver 288 may be adapted to allow mobile device 100 to directly queryOCSP server 286 to verify the revocation status of certificates.

It will be understood by persons skilled in the art that mobile dataserver 288 need not physically reside on a separate computing devicefrom the other components of LAN 250, and that mobile data server 288may be provided on the same computing device as another component of LAN250 in variant implementations. Furthermore, the functions of mobiledata server 288 may be integrated with the functions of anothercomponent in LAN 250 (e.g. message management server 272) in variantimplementations.

In variant implementations, only selected PKI servers 280 may be madeaccessible to mobile devices (e.g. allowing certificates to bedownloaded only from a user's computer 262 a, 262 b, while allowing therevocation status of certificates to be checked from mobile device 100).

In variant implementations, certain PKI servers 280 may be madeaccessible only to mobile devices registered to particular users, asspecified by an IT administrator, possibly in accordance with an ITpolicy, for example.

Other sources of certificates [not shown] may include a Windowscertificate store, another secure certificate store on or outside LAN250, and smart cards, for example.

Referring now to FIG. 6, a block diagram illustrating components of anexample of an encoded message, as may be received by a message server(e.g. message server 268 of FIG. 4), is shown generally as 350. Encodedmessage 350 typically includes one or more of the following: a headerportion 352, an encoded body portion 354, optionally one or more encodedattachments 356, one or more encrypted session keys 358, and signatureand signature-related information 360. For example, header portion 352typically includes addressing information such as “To”, “From”, and “CC”addresses, and may also include message length indicators, and senderencryption and signature scheme identifiers, for example. Actual messagecontent normally includes a message body or data portion 354 andpossibly one or more attachments 356, which may be encrypted by thesender using a session key. If a session key was used, it is typicallyencrypted for each intended recipient using the respective public keyfor each recipient, and included in the message at 358. If the messagewas signed, a signature and signature-related information 360 are alsoincluded. This may include the sender's certificate, for example.

The format for an encoded message as shown in FIG. 6 is provided by wayof example only, and persons skilled in the art will understand thatembodiments of the invention will be applicable to encoded messages ofother formats. Depending on the specific messaging scheme used,components of an encoded message may appear in a different order thanshown in FIG. 6, and an encoded message may include fewer, additional,or different components, which may depend on whether the encoded messageis encrypted, signed or both.

Embodiments of the invention are generally directed to a system andmethod for searching and retrieving certificates. In one embodiment, acertificate search application residing and executing on a mobile device(e.g. mobile device 100 of FIG. 4) is programmed to initiate certificatesearches on one or more certificate servers (e.g. LDAP server 284 ofFIG. 4). In this embodiment, the mobile device searches for andretrieves certificates from a certificate server through an intermediatecomputing device (e.g. mobile data server 288 of FIG. 4).

With reference to FIG. 4, consider an example implementation where acertificate search application on mobile device 100 searches for andretrieves individual certificates from LDAP server 284 through mobiledata server 288. A search request is received by the certificate searchapplication, typically from a user who provides a first name, last name,and e-mail address of an individual for whom the user wishes to locate acertificate. Certain search requests may also be made broader, byconstructing search queries where inputting only a few letters of a namewill return all certificates issued with a name containing those lettersas a prefix, or by otherwise using wild cards or blank entries in inputfields to expand a search, for example. The search request is thencommunicated from mobile device 100 to mobile data server 288, whichthen queries LDAP server 284 for the requested certificate(s). In thisexample implementation, located certificates are retrieved by the mobiledata server 288, and specific search result data relating to eachretrieved certificate, such as the common name and e-mail address of theindividual (or entity) to which the respective certificate is issued, iscommunicated to the mobile device 100 so that a list can be generatedfrom the search result data for display to the user. The user can thenselect specific certificates for downloading to and storage on mobiledevice 100 from the list. The selections are then communicated to mobiledata server 288, from which the selected certificates are downloaded tomobile device 100.

When a user of mobile device 100 receives a signed message from asender, the certificate of the sender is required in order to verify theintegrity of the message and authenticate the identity of the sender.This certificate may also be referred to herein in the specification andin the claims as a “sender certificate” or “sender's certificate”.Consider the situation where only a part of the received message hasbeen downloaded to mobile device 100, for viewing by a user through amessaging application executing and residing on mobile device 100. Thepart of the message received likely includes header information (e.g.header 352 of FIG. 6) from which at least the sender's e-mail addresscan typically be obtained. However, the part of the message received bymobile device 100 might not include the sender's certificate oridentifiers that can be used to identify the requisite certificate,since such signature-related information is typically attached near theend of a message (see e.g., signature and signature-related information360 of FIG. 6).

The certificate search application on mobile device 100 can be activated(e.g. by the user selecting an appropriate menu option made accessiblewhen the message is being viewed) to download the sender's certificate.Since the sender's e-mail address can be obtained from the downloadedheader information, the certificate search application can automaticallyinitiate a search for certificates having a matching e-mail address, onone or more certificate servers (e.g. LDAP server 284) through themobile data server 288. In particular, where the message is notaccompanied by the sender's certificate, the certificate may need to beretrieved from a certificate server by the certificate searchapplication.

However, multiple certificates matching the specified e-mail address maybe located by the search. In prior art systems, if the part of themessage containing the necessary information to correctly identify therequisite certificate associated with that message was not downloaded tomobile device 100, the user may not be able to select the correctcertificate from a list identifying the multiple certificates located inthe search with certainty. The user would then have to guess at thecorrect certificate, or download all the located certificates forstorage on the mobile device, which consumes time and bandwidth. Similarproblems may arise where data other than an e-mail address is retrievedfrom a message and used to perform a certificate search.

Accordingly, embodiments of the invention relate generally to methodsthat can facilitate a determination of the certificate associated with amessage, from a plurality of certificates located in a search of one ormore certificate servers, even where a message has not been downloadedin its entirety to a user's computing device (e.g. mobile device).

Referring to FIG. 7A, a flowchart illustrating steps in a method ofsearching and retrieving certificates in an embodiment of the inventionis shown generally as 400.

At step 410, a message addressed to the user of a computing device (e.g.mobile device 100 of FIG. 4) is received at a message server (e.g.message server 268 of FIG. 4). In one example implementation, a messagemanagement server (e.g. message management server 272 of FIG. 4) pushesa first part of the received message stored on the message server to amobile device. The message management server can deliver further partsof the received message at the request of the user, possibly up to amaximum pre-defined message size. The message parts delivered to themobile device will generally include header information (e.g. header 352of FIG. 6), which is typically provided at the beginning of a message.

In embodiments of the invention, the message management server addscertificate identification data to the delivered message parts (e.g. tothe header of the message). If a certificate accompanies the receivedmessage, then the message management server can process the certificateto generate the certificate identification data. In one embodiment, themessage management server applies a hash algorithm to hash at least apart of the certificate. The hash is then used as the certificateidentification data to be added to the message parts (e.g. header) beingdelivered to the mobile device. In one implementation, the entirecertificate is hashed to generate the hash. However in variantimplementations, one or more specific parts or fields of a certificatemay be hashed to generate the hash, although the likelihood that thehash will uniquely and correctly identify an identical certificate maybe decreased depending on the parts or fields hashed.

In another embodiment, the message management server processes thecertificate accompanying the received message, by parsing thecertificate to identify the serial number and issuer of the certificate.This serial number and issuer data is then used as the certificateidentification data to be added to the message parts (e.g. header) beingdelivered to the mobile device.

Similarly, where the sender's certificate does not accompany thereceived message, the message management server may parse thesignature-related information in the message to retrieve data thatidentifies the sender's certificate associated with the message, such asthe serial number and issuer of the certificate used to sign themessage, for example. This data is then used as the certificateidentification data to be added to the message parts (e.g. header) beingdelivered to the mobile device.

In some applications, use of the serial number and issuer data from acertificate as certificate identification data might be considered to beless secure, when compared to the use of a hash of an actual certificate(which certificate can be validated as described with reference to FIG.5), since the serial number and issuer data may be easier to forge.However, use of either type of certificate identification data may beuseful in variant implementations, depending on the level of securitydesired.

The generated certificate identification data can be used to uniquelyidentify the sender's certificate associated with the received message.This may be particularly useful when the actual signature andsignature-related information of the received message (e.g. signatureand signature-related information 360 of FIG. 6) has not been deliveredto the mobile device.

At step 420, a messaging application residing and executing on themobile device receives one or more parts of the received message, whichincludes the certificate identification data, from the messagemanagement server. Additional parts of the received message may beretrieved from the message management server in response to a userrequest.

Optionally, at step 430, the messaging application can use thecertificate identification data received from the message managementserver to determine whether the certificate associated with the receivedmessage is already stored on the mobile device in one or more designatedcertificate stores thereof. A corresponding indication of whether or notthe certificate is already stored may be provided with the messagepart(s) being displayed, or alongside an entry where the message isidentified in a list of messages received by the user, for example.

For example, in an embodiment where the certificate identification datacomprises a hash, at step 430, the messaging application generates ahash for each certificate stored on the mobile device in one or moredesignated certificate stores thereof, and compares each generated hashto the hash provided as certificate identification data, in order todetermine whether the certificate is already stored on the mobiledevice. The same hash algorithm employed at step 410 is applied at thisstep (to the same parts or fields of the stored certificates if theentire certificates are not hashed) in generating the hashes of thestored certificates. Accordingly, if a generated hash of a given storecertificate matches the hash received from the message managementserver, then a match is deemed to have been determined.

Alternatively, in an embodiment where the certificate identificationdata comprises serial number and issuer data, at step 430, the messagingapplication compares the serial number and issuer data associated witheach certificate stored on the mobile device in one or more designatedcertificate stores thereof to the serial number and issuer data providedas certificate identification data, in order to determine whether thecertificate is already stored on the mobile device.

In variant implementations, step 430 may be performed by an applicationresiding and executing on the mobile device other than the messagingapplication (e.g. by a certificate search application).

At step 440, a search request for the certificate is made by acertificate search application residing and executing on the mobiledevice. For example, the search request may be initiated by a user, whoselects a menu option provided by the messaging application thatactivates the certificate search application. Alternatively, themessaging application or some other application on the mobile device mayautomatically activate the certificate search application, uponreceiving a message for example, and possibly after determining that thecertificate is not already stored on the mobile device at step 430.

In requesting a certificate search at step 440, the certificate searchapplication transmits the search request to at least one certificateserver (e.g. LDAP server 284 of FIG. 4) through a mobile data server(e.g. mobile data server 288 of FIG. 4) in one example implementation.The search request comprises data that typically includes an e-mailaddress, and possibly at least one name associated with the sender ofthe received message. However, it will be understood by persons skilledin the art that a variety of search queries may be constructed withoutdeparting from the scope of the invention.

At step 450, the mobile data server queries the at least one certificateserver for certificates satisfying the search request that was made atstep 440 by the certificate search application of the mobile device.Certificates located as a result of the search query are retrieved fromthe at least one certificate server by the mobile data server.

At step 460, the located certificates are downloaded to the mobiledevice from the mobile data server. The downloaded certificates aretypically stored temporarily on the mobile device to undergo furtherprocessing.

At step 470, the located certificates downloaded to the mobile device atstep 460 are processed by the certificate search application, todetermine which located certificate, if any, matches the certificateassociated with the received message, as identified by the certificateidentification data accompanying the received message.

In an embodiment where the certificate identification data comprises ahash, the certificate search application generates a hash for eachlocated certificate, and compares each generated hash to the hashprovided as certificate identification data, in order to determine theproper match. The same hash algorithm employed at step 410 is applied atthis step (to the same parts or fields of the stored certificates if theentire certificates are not hashed) in generating the hashes of thestored certificates. Accordingly, if a generated hash of a given locatedcertificate matches the hash provided as certificate identificationdata, then a match is deemed to have been determined.

Alternatively, in an embodiment where the certificate identificationdata comprises serial number and issuer data, the certificate searchapplication compares the serial number and issuer data associated witheach located certificate to the serial number and issuer data providedas certificate identification data, in order to determine the propermatch.

Optionally, at step 480, a list identifying the located certificatesdownloaded at step 460 may be displayed to a user, with an indicator orother highlighting technique used to identify the matching certificatein the list. The user may then be prompted to select the matchingcertificate (and possibly other located certificates) to be stored in acertificate store on the mobile device for future use.

At step 490, the matching certificate is stored in a certificate storeon the mobile device. In one embodiment, this step may be performedautomatically by the certificate search application, without prompting auser for its selection at step 480.

In a variant embodiment, the matching certificate may also be validated[step not shown], to verify its trust status for example, before orafter storage.

Referring now to FIG. 7B, a flowchart illustrating steps in a method ofsearching and retrieving certificates in another embodiment of theinvention is shown generally as 400 b. Method 400 b is similar to method400, except that the certificate search application may pass thecertificate identification data to the mobile data server (e.g. with thesearch request), so that the mobile data server can return only thematching certificate to the mobile device, instead of all of thecertificates located in the search.

Specifically, at step 440, the certificate identification data initiallyreceived at the mobile device from the message management server isforwarded to the mobile data server with the search request, in thisembodiment of the invention.

At step 460 b, the mobile data server processes the located certificatesto determine which located certificate matches the certificateassociated with the received message, as identified by the certificateidentification data received at the mobile data server from the mobiledevice at step 440. Only the matching certificate is then downloaded tothe mobile device at this step, for subsequent storage in a certificatestore on the mobile device at step 490. The user may be prompted forpermission to save the matching certificate before storage [step notshown].

Details pertaining to the remaining steps shown in FIG. 7B are providedwith reference to FIG. 7A.

In variant embodiments of the invention, other data that can be used touniquely identify a certificate can be employed as certificateidentification data.

In a variant embodiment of the invention, located certificates may beretrieved from one or more certificate servers and downloaded to amobile device without being transmitted via a mobile data server orother intermediate computing device.

Embodiments of the invention have been described above with reference toa mobile device. However, some embodiments may also be applied to adevice that is adapted to receive encoded messages other than a mobiledevice.

The steps of a method of searching and retrieving certificates inembodiments of the invention may be provided as executable softwareinstructions stored on computer-readable media, which may includetransmission-type media.

The invention has been described with regard to a number of embodiments.However, it will be understood by persons skilled in the art that othervariants and modifications may be made without departing from the scopeof the invention as defined in the claims appended hereto.

1. A method of searching and retrieving certificates relating to amessage received from a sender, the message comprising a first part anda second part, the first part comprising a header and a message body ofthe message, and the second part comprising data identifying a sendercertificate associated with the message, wherein the method comprises:at a computing device, receiving, at least some data of the first partof the message but not of the second part of the message, wherein the atleast some data of the first part of the message contains firstcertificate identification data that uniquely identifies the sendercertificate; performing a search on one or more certificate servers,wherein at least one query is submitted to the one or more certificateservers to request retrieval of certificates satisfying a certificatesearch request; retrieving at least one certificate satisfying thecertificate search request from the one or more certificate servers; andprocessing each retrieved certificate using the first certificateidentification data to determine if any of the retrieved at least onecertificate is the sender certificate associated with the message. 2.The method of claim 1, wherein the processing comprises: generatingsecond certificate identification data associated with each retrievedcertificate; and comparing the generated second certificateidentification data for each retrieved certificate to the firstcertificate identification data contained in the at least some data ofthe first part of the message, to identify a certificate of the at leastone retrieved certificate matching the sender certificate.
 3. The methodof claim 1, wherein the message is received via a server remote from thecomputing device, and wherein the first certificate identification datawas added to the message by the server.
 4. The method of claim 2,wherein the generated second certificate identification data associatedwith each retrieved certificate comprises a serial number and issuerdata for the certificate; and wherein the generating second certificateidentification data comprises parsing each retrieved certificate toobtain the serial number and issuer data for the certificate.
 5. Themethod of claim 2, wherein the generated second certificateidentification data associated with each retrieved certificate comprisesa hash of at least a part of the certificate; and wherein the generatingsecond certificate identification data comprises applying a hashalgorithm to each retrieved certificate to obtain the hash for thecertificate.
 6. The method of claim 1, wherein the computing devicecomprises a mobile device.
 7. The method of claim 6, wherein theperforming and retrieving are initiated at a second computing devicecoupled to the mobile device.
 8. The method of claim 7, wherein thesecond computing device comprises a mobile data server.
 9. The method ofclaim 7, wherein the processing is performed at the second computingdevice, and wherein the method further comprises downloading, to themobile device from the second computing device, a certificate of the atleast one retrieved certificate if the certificate is the sendercertificate associated with the message.
 10. The method of claim 7,wherein the processing is performed at the mobile device, and whereinthe method further comprises downloading each retrieved certificate tothe mobile device from the second computing device.
 11. The method ofclaim 1, further comprising storing a certificate of the at least oneretrieved certificate on the computing device, if the certificate is thesender certificate associated with the message.
 12. A system forsearching and retrieving certificates relating to a message receivedfrom a sender, the message comprising a first part and a second part,the first part comprising a header and a message body of the message,and the second part comprising data identifying a sender certificateassociated with the message, the system comprising: a first computingdevice configured to: receive at least some data of the first part ofthe message but not of the second part of the message, wherein the atleast some data of the first part of the message contains firstcertificate identification data that uniquely identifies the sendercertificate; and a second computing device; wherein at least one of thefirst computing device and the second computing device is configured to:perform a search on one or more certificate servers, wherein at leastone query is submitted to the one or more certificate servers to requestretrieval of certificates satisfying a certificate search request; andretrieve at least one certificate satisfying the certificate searchrequest from the one or more certificate servers; and wherein at leastone of the first computing device and the second computing device isfurther configured to process each retrieved certificate using the firstcertificate identification data to determine if any of the retrieved atleast one certificate is the sender certificate associated with themessage.
 13. The system of claim 12, wherein when processing eachretrieved certificate, the at least one of the first computing deviceand the second computing device is further configured to: generatesecond certificate identification data associated with each retrievedcertificate; and compare the generated second certificate identificationdata for each retrieved certificate to the first certificateidentification data contained in the at least some data of the firstpart of the message, to identify a certificate of the at least oneretrieved certificate matching the sender certificate.
 14. The system,of claim 12, wherein the message is received via a server remote fromthe computing device, and wherein the first certificate identificationdata was added to the message by the server.
 15. The system of claim 13,wherein the generated second certificate identification data associatedwith each retrieved certificate comprises a serial number and issuerdata for the certificate; and wherein when generating the secondcertificate identification data, the at least one of the first computingdevice and the second computing device is further configured to parseeach retrieved certificate to obtain the serial number and issuer datafor the certificate.
 16. The system of claim 13, wherein the generatedsecond certificate identification data associated with each retrievedcertificate comprises a hash of at least a part of the certificate; andwherein when generating the second certificate identification data, theat least one of the first computing device and the second computingdevice is further configured to apply a hash algorithm to each retrievedcertificate to obtain the hash for the certificate.
 17. The system ofclaim 12, wherein the first computing device comprises a mobile device.18. The system of claim 12, wherein the second computing devicecomprises a mobile data server.
 19. The system of claim 12, wherein thesecond computing device processes each retrieved certificate, andwherein the first computing device is further configured to downloadfrom the second computing device, a certificate of the at least oneretrieved certificate if the certificate is the sender certificateassociated with the message.
 20. The system of claim 12, wherein thefirst computing device processes each retrieved certificate, and whereinprior to the processing, the first computing device is furtherconfigured to download each retrieved certificate to the first computingfrom the second computing device.
 21. The system of claim 19, whereinthe first computing device is further configured to store thecertificate.
 22. A non-transitory computer-readable medium storinginstructions for execution on at least one of a first computing deviceand a second computing device, the instructions for performing a methodof searching and retrieving certificates relating to a message receivedfrom a sender, the message comprising a first part and a second part,the first part comprising a header and a message body of the message,and the second part comprising data identifying a sender certificateassociated with the message, wherein when the instructions are executed,the first computing device: receives at least some data of the firstpart of the message but not of the second part of the message, whereinthe at least some data of the first part of the message contains firstcertificate identification data that uniquely identifies the sendercertificate; at least one of the first computing device and the secondcomputing device: performs a search on one or more certificate servers,wherein at least one query is submitted to the one or more certificateservers to request retrieval of certificates satisfying a certificatesearch request; and retrieves at least one certificate satisfying thecertificate search request from the one or more certificate servers; andat least one of the first computing device and the second computingdevice processes each retrieved certificate using the first certificateidentification data to determine if any of the retrieved at least onecertificate is the sender certificate associated with the message.